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Chemical and bacterial reduction of azo-probes: monitoring a conformational change using fluorescence spectroscopy

Rattray, Nicholas J.W., Zalloum, Waleed A., Mansell, David, Latimer, Joe, Jaffar, Mohammed, Bichenkova, Elena V., Freeman, Sally
Tetrahedron 2013 v.69 pp. 2758-2766
Clostridium perfringens, Escherichia coli, bacteria, biomimetics, chemical reactions, chemical structure, enzymes, fluorescence, fluorescence emission spectroscopy, monitoring, organic compounds
Sterically constrained probes 2,4-O-bisdansyl-6,7-diazabicyclo[3.2.1]oct-6-ene (8) and 2,4-O-bispyrenoyl-6,7-diazabicyclo[3.2.1]oct-6-ene (9) exhibit specific dimer fluorescent characteristics (λmax 555 nm and 511 nm, respectively), attributed to the 2,4-diaxial arrangement of the dansyl or pyrene groups. Reduction of the azo-conformational locking group in (8) and (9) yielded 1,3-bisdansyl-4,6-diaminocyclohexane (16) and 1,3-bispyrenoyl-4,6-diaminocyclohexane (17) in the tetra-equatorial chair conformation, thus minimising interaction of the bisdansyl or bispyrenoyl groups. This induces a change in fluorescence from a cooperative green emission dimer band to a blue-shifted, monomer type fluorescence, with λmax 448 nm and 396 nm for the reduced forms (16) and (17), respectively. The azo-bond conformational lock can either be reduced under biomimetic conditions (using sodium dithionite) or with bacteria (Clostridium perfringens or Escherichia coli) utilising azo-reductase enzymes. These fluorescent probes have the potential to specifically detect azo-reductase expressing bacteria.